CAT 2021 Slot 1 · Quant · Question 22
CAT 2021 Slot 1 previous year question on Sequences and Series, with the answer and a step-by-step solution.
The natural numbers are divided into groups as (1), (2, 3, 4), (5, 6, 7, 8, 9), ... and so on. Then, the sum of the numbers in the 15th group is equal to
- A
4941
- B
6090
- C
6119
- D
7471
Pick an option, then check.
Answer & solution
Answer: Option C
The k-th group has 2k-1 terms and ends at {k}^{2}.
For k=15 the last term is 225 and the group has 29 terms, so it starts at 225-28=197. The sum is \frac{29}{2}\left( 197+225 \right)=29\times 211=6119.
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